How do I change number of columns in a proper way in twentyfourteen child theme?

I’m not sure why you are using exit() in yourreactivatejs()` method as this breaks the method before it even loads your script (hopefully this is for debugging purposes).

I also do think that in is unnecessary to create a class to this, a simple spaghetti function would do perfectly. Anyways, if you need to use a class, the class’s constructor is not suppose to any work, the constructor is suppose to initialize the class. You would want to to take your action outside of the constructor. Also, when it comes to removing scripts and styles, you would want to deregister and dequeue.

Here are possible solutions:

CLOSURES – not really recommended as they cannot be removed

add_action( 'wp_enqueue_scripts', function ()
{
    // Remove your script
    wp_dequeue_script( 'twentyfourteen-script' );
    wp_deregister_script( 'twentyfourteen-script' );

    // Add new script
    wp_enqueue_script( 'lets-be-unique-here', get_stylesheet_directory_uri() . '/js/functions.js', ['jquery'], '20140616', true );
}, 100 );

NORMAL SPAGHETTI

add_action( 'wp_enqueue_scripts', 'addjs', 100 );
function addjs()
{
    // Remove your script
    wp_dequeue_script( 'twentyfourteen-script' );
    wp_deregister_script( 'twentyfourteen-script' );

    // Add new script
    wp_enqueue_script( 'lets-be-unique-here', get_stylesheet_directory_uri() . '/js/functions.js', ['jquery'], '20140616', true );
}

CLASS WITH ACTION OUTSIDE

class AddJS
{
    public function addjs ()
    {
        // Remove your script
        wp_dequeue_script( 'twentyfourteen-script' );
        wp_deregister_script( 'twentyfourteen-script' );

        // Add new script
        wp_enqueue_script( 'lets-be-unique-here', get_stylesheet_directory_uri() . '/js/functions.js', ['jquery'], '20140616', true );
    }
}

THEN

add_action( 'wp_enqueue_scripts', ['AddJS','addjs'], 100 );

OR

$addjs = new AddJS();
add_action( 'wp_enqueue_scripts', [$addjs,'addjs'], 100 );

CLASS WITH ACTION INSIDE CLASS

class AddJS
{
    public function addAction ()
    {
        add_action( 'wp_enqueue_scripts', [$this,'addjs'], 100 );
    }

    public function addjs ()
    {
        // Remove your script
        wp_dequeue_script( 'twentyfourteen-script' );
        wp_deregister_script( 'twentyfourteen-script' );

        // Add new script
        wp_enqueue_script( 'lets-be-unique-here', get_stylesheet_directory_uri() . '/js/functions.js', ['jquery'], '20140616', true );
    }
}
$addjs = new AddJS();
$addjs->addjs();